Democratic lawmakers introduced federal legislation Thursday that would ban defense contractors and government-owned plants from selling high-caliber ammunition to civilians.

Sens. Elizabeth Warren (D-Mass.) and Andy Kim (D-Calif.), and Reps. Robert Garcia (D-Calif.) and Jamie Raskin (D-Md.) co-sponsored the bill, which would also prevent the Pentagon’s contractors from selling assault weapons to the public.

The action follows an investigation by ICIJ and the New York Times that revealed that .50-caliber ammunition made at a facility owned by the U.S. Army has been trafficked to cartels who used it to wage war against the Mexican government.

“Americans’ tax dollars should not be used to fuel gun violence,” Warren said in a statement. “Congress must step in to keep Americans safe, and that means stopping the U.S. military and giant defense contractors from selling weapons of war to cartels, criminal groups, and mass shooters that terrorize our communities.”

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The ammunition was made by government contractors at the Lake City Army Ammunition Plant outside of Kansas City, Missouri. The plant is the largest producer of rifle rounds for the U.S. government and its allies and has produced billions of rounds of ammunition that have been sold on the civilian market.

That has included .50 caliber ammunition as large as a medium-sized cigar and capable of penetrating armored vehicles The cartridges are designed for use by the military and have limited civilian application.

ICIJ’s investigation found that cartels had purchased large quantities of the ammunition from civilian dealers and then smuggled them into Mexico where they have added to the criminal organizations’ massive firepower.

Cartel gunmen armed with .50-caliber firearms have downed helicopters, assassinated government officials, shot at police and military forces and massacred civilians.

Americans’ tax dollars should not be used to fuel gun violence.

— Senator Elizabeth Warren

In February, Mexico’s defense minister told reporters that nearly half of the .50-caliber ammunition seized by the Mexican government was inscribed with Lake City’s mark.

The ICIJ identified four instances of .50-caliber Lake City casings being recovered at crime scenes linked to cartel violence. In one case, armor-piercing ammunition made at the facility penetrated an armored vehicle, killing one crew member and wounding three others.

The investigation found that at least 16 online retailers in the U.S. have sold the ammunition despite previous efforts by Congress to stop it from getting into the public’s hands.

Lake City also produces a smaller round made for the popular AR-15 semiautomatic rifle that is  routinely found at crime scenes involving AR-15s in the U.S., ICIJ and the New York Times revealed in November.

Although Lake City is owned by the U.S. government, it is operated by private contractors. The U.S. Army has allowed them to manufacture products for the commercial market under an agreement that is intended to reduce costs for the military and to guarantee that the facility continues to run even when military demand for ammunition wanes.

Republican officials have argued that the arrangement is vital both to national security and to ensuring the supply of cheap ammunition to the public.

In a 2024 letter addressed to then President Joe Biden, Republican attorneys general from 28 states opposed efforts to stop commercial production at Lake City, writing that, “Our country needs to be prepared to face foreign adversaries rather than focusing on destroying the Second Amendment and crippling the firearm and ammunition market.”

Democratic lawmakers had previously introduced a bill aimed at stopping sales of Lake City ammunition to civilians, but it never came to a vote.

They hope that this time will be different. “We should not live in a world where weapons and ammunition sold by the government end up in the hands of violent criminals and are used to devastate our own communities,” said Congressman Robert Garcia in a statement.